1. Field of the Invention
The present invention relates to an ink jet ink set and an ink jet recording method.
2. Description of the Related Art
Recording can be made on various recording media by an ink jet recording method. To produce better images, various inks, such as inks suitable to record photo-quality images on glossy paper and so forth and inks suitable to record documents on plain paper and so forth, have been reported for any purpose.
In recent years, the ink jet recording method also has been employed to print business documents including characters and diagrams on, for example, plain paper as a recording medium. The ink jet recording method has become increasingly employed for such applications. In such applications, importance is placed on the high-speed printing of clear images on a recording medium, such as plain paper. Thus, inks are required to provide an image having an excellent optical density, to have high drying speed (good fixability), and to be able to reduce bleeding between inks.
To solve these technical problems, proposals focused on the relationship of the physical properties between a plurality of inks are made (see Japanese Patent Laid-Open Nos. 2008-308664 and 2004-338392). Japanese Patent Laid-Open No. 2008-308664 discloses a set of a pigment ink containing a salt of a monovalent anion and a pigment to raise the dynamic surface tension at a lifetime of 50 msec and a dye ink. The document also states that ink droplets are present on a surface of a recording medium and that the destabilization of the dispersion state of the pigment is promoted by the effect of the salt while water evaporates, to aggregate the pigment, thereby providing a high optical density. Furthermore, the document states that the aggregation of the pigment is less likely to be mixed with the dye ink, thus improving the bleeding resistance. Japanese Patent Laid-Open No. 2004-338392 discloses that an ink set specifies the relationship of the contact angle of a plurality of inks that can react with each other so as not to easily mix the plurality of inks together. The document also states that a fluorinated surfactant is incorporated into one ink in order to satisfy the relationship of the contact angle, thereby increasing the water repellency of a region of a recording medium to which the ink is applied and inhibiting the spreading of the other ink to be applied to the region.
Moreover, proposals regarding the incorporation of fluorinated surfactants into inks are made (see Japanese Patent Laid-Open Nos. 2003-335987 and 2001-335725). Japanese Patent Laid-Open No. 2003-335987 discloses that even when the viscosity of an ink is increased in order to reduce bleeding, a decrease in the surface tension of the ink with a fluorinated surfactant having a specific structure ensures the ejection stability of the ink and improves the drying properties of an image. Japanese Patent Laid-Open No. 2001-335725 discloses that the incorporation of a fluorinated surfactant into an ink used for the recording on glossy paper reduces the solidification of the ink in a recording head and the bleeding of an image and shortens the drying time.